Identification is important. Clarity is important. Avoiding ambiguity is important.
With those things in mind, when identifying individuals on pictures, on family ephemera, in writings, etc. avoid using only the word “Grandma,” “Grandpa,” “Aunt,” etc.
After all, to which Grandma Neill are you referring? Your Grandma? Your Dad’s Grandma? Your children’s Grandma? If you want to use Grandma at least use the individual’s complete name after the use of the term, Grandma Ida (Trautvetter) Neill, Grandma Connie (Ufkes) Neill, etc.
Also avoid using abbreviations if at all possible, particularly ones that you’ve created yourself. Will someone else know what you meant?